Means for relieving telephone-lines from deleterious electrical charges.



No. 657,305. L Patented se t. 4, I900: c. H.ARNOLD. MEANS FOR RELIEVING TELEPHONE LINES FROM DELETERIOUS ELECTRICAL C H 'A R G E S (Application filed Dec. 22, 1899.)

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UNITED STATES.

PATENT I G EIGE.

CHESTER rLA noLD, 0F Eos'ron, MASS GH SETTS, ASSIGNOR TO-THE AMERICAN BELL TELEPHONE COMPANY, OF SAME PLACE.

MEANS FOR RELIEVING TELEPHONE-LIN ES FROM DELETERIOUS ELECTRICAL CHARGES.

SPECIFICATION forming part of Letters Patent No. 657,305, dated September 4, 1900. Application filed December 22, 1899. Serial No. 741,269. No model-J To all whom, it may concern:

Be it known that I, CHESTER H. ARNOLD, residing at Boston, in the county of Suffolk and State of Massachusetts, have invented certain Improvements in Means for Freeing Telephone-Lines from Deleterious Electrical Charges, of which the following is a specification.

'This invention relates to metallic-circuit telephone-lines, and especially to such as extend between stations a considerable distance apart, and more particularly concerns the application to such lines of means for freeing interfere seriously with telephonic communi cation they are always in the highest degree undesirable, since by reason of their pres ence users of the telephone and employees are exposed to unpleasant and possibly dangerous shocks, while their discharge, if uhprovided for, is likely to be detrimental to apparatus, such as space cut-outs and protective appliances, which are subject to injury from incessant sparking due to these charges and their disruptive escape.

The object of this invention, stated in a general way, is to reduce the potential of the line conductors to approximately that of the earth,

and thereby to remedy these and other harm ful results incident to the presence of excess:- ive potentials on telephone-circuits, or, in other words, it is to provide a simple means for clearing the line conductors of these intrusive and detrimental charges without at the same time diminishing the volume of the legitimate working current or involving any material escape thereof. In the invention a metallic-circuit or double-wire telephone line is provided at one or more points between its end stations with an electromag netic coil or helix Wound on a normally-unanceless earth conductor is attached to its center, thus providing a dead ground conductor connection at the middle of the coil. The device as a whole when thus connected constitutes a leak from both line conductors at the same point to earth, the, discharge of each conductor passing by Way of its own half-of the electromagnetic winding, while with respect to the said two line conductors considered as the two sides of the telephonecircuit it constitutes merely a bridge containing the whole of the electromagnetic winding, the ground connection from this point of view being functionless. The intrusive charge passing from both conductors simultaneously traverses the two halves of the coil in opposite directions and discharges to earth at the middle thereof, acting to maintain absolute magnetic neutrality in the normallyunmagnetized core; but the voice-currents or other legitimate working currents of the telephone cannot pass from oneside of the circuit to the other through the discharging device Without traversing the whole of the winding around the core at any given moment in the same direction, thus tending to set-up N polarity at one end of the normally-unmagnetized core and S polarity at the other end thereof, and therefore producing maximum impedance to the passage of the voice or working currents. Hence the said device while having a low impedance to the detrimental charges infesting the line has a high impedance as regards the Working current, so that While the passage of the said undesired charges from both line conductors is greatly facilitated (the said conductors being practically at all times freed therefrom) there is no material loss of working current.

In the drawings which accompany this specification, Figure 1 is a diagram representinga metallic-circuit telephone-line extend 7 ing between two stations and shown as being provided with the discharging device, which I combined withthe said line constitutes my invention. Fig. 2 represents a .portion of I such a telephonescircuit and a preferred form of electromagnetic coilassociated therewith. I In'the drawings, L is the metallic-circuittelephone-line having main conductorsA and B and extending between stations X and Z,

' at each of which are placed the usual 'tele the core. coil employed in the claims is to be underph0ne-receiver t and transmitter'T, the lat-J ter being included, with its battery b, in a localcircuit d,-associate'd withthe main circuit'by'm'eans of theinduction-coil I in a manner well understood.

M is an electromagnetic coil consisting of a helix of insulated wire is, wound over a normally-unmagnetized single or homogeneous ron core 0, preferably formed, as indicated in Fig. 2, with'a closed magnetic circuit, In

Fig. 2 the helix or corek is formed in two sections, together constituting a singlecoil wound continuously in one direction only on The term single electromagnetic I stood as including such a coil; In Fig. 1 two coils are shown as being applied to the mainline circuit L at points'C and B, respectively, and one, two, or more may be so employed; but in most cases a single coil applied as shown is sufiicient.

' conductor or ground connection g, extending from the center a; of its winding to earth at G. The working current of the circuit considered at any given moment traverses the two main conductors in opposite directions, as indicated by the feathered arrows, while the charges which are to be dissipated being at any given moment of the same sign in both conductors areindicated by the plain arrows. It is manifest that the working current or any portion thereof passing from the main conductor A to the other, B, or vice versa,;by

way of the bridge-wires to 'must necessarily traverse the entire coil is and that the impedance oifered thereby will be high, the tendency being to set up N polarity at one end of the normally-unmagnetized core and S polarity at the other end thereof, and also that the dissipation of the deleterious charge of con ductors A and B, respectively, at any bridge to will be oppositely directed within the coilwinding 10, the discharge from a passing through the half It and that of B through the half h of the winding to the central ground connection, thus acting to maintain absolute magnetic neutrality in the normally-unmagnetized core, the impedance of such a path being low. Good results have been attained with a coil containing as a whole two thousand'turns of wire, forming a resistance for each half-coil between the line conductor with which it connects and the ground offseventeen ohms.

vI am aware that heretoforebranches ex.-

tending independently to earth from the two line conductors}respectively, of a metallic circuit and each containing'an independent electromagnetic coil having a separate iron core of itsown have been employed for the purpose of diminishingthe static charge of the line. has a high impedance for the dissipation of "the. deleterious charge, 'aswell as for the working current, and is therefore not adapted for the pur oses specified herein. My invention diifers from such an arrangement both in structur'e'and operation, since it comprehends a single split coil wound on a s1ngle core and provided with-a centrally-connectedearth branch and serves to clear both sides of the line at once, the discharge cur- .rents or-impulses passing simultaneously through the two halves of the coil oppositely, the magnetic eifect which each would tend toexercise on the common core being thus neutralized by the equal and opposing effect of the other. The impedance of the connection between the two line-conductors as a unit and the earth is thus much less than if separate coils were used for each line con ductor. v I claim as my invention l. The combination with a metallic-circuit telephone-line; of means for freeing the conductors of said line from intrusive and detrimental' electrical charges, said means con 'sisting of a bridge between the main conductors of said line containing only a single electromagnetic coil wound continuously in one direction, and a resistanceless ground connection centrally attached to the said coil; and constituting a leak to earth from both conductors at the same point,'oflfering low impedance to the said charges, but high impe- In testimony whereof I have signed my name to this specification, in the presence of two subscribing witnesses, this 9th day of December, 1899.

CHESTER H. ARNOLD.

Witnesses: 1 v GE WILLIS PIERCE, JOSEPH A. GATELY;

Such a coil so connected, however, 

